Fisheries stocks from an ecological perspective: Disentangling ecological connectivity from genetic interchange

Abstract

The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for the fisheries science. Methods for delimiting stocks have advanced considerably over recent years, using including genetic, tagging and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can delimited as management units if there limited exchange during recruitment or via migration in most years. However from a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

Disentangling the genetic and morphological structure of Patella candei complex in Macaronesia (NE Atlantic)

“…Whether this would facilitate current taxonomic misinterpretations and conservation needs, further research is still required, especially in diagnosing intrinsic reproductive isolation (Frankham et al., ). Ultimately, this elevation of subspecies to species level would be in agreement with stock delimitation and units of conservation (Hawkins et al., ) with potential benefits for management plans aimed at the preservation of limpets stocks across the Macaronesia region.…”

“…At multiple spatial scales, we evaluate the degree of contemporary connectivity among populations and hypothesize that populations geographically closer to each other are likely more related and connected via larval dispersion. Besides the assessment of genetic diversity and structure of P. candei populations across archipelagos, and given the importance of defining conservation units in fisheries planning (Hawkins et al., ), we provide discussion and guidance about protective measures of such threatened marine resource, highlighting the importance of considering levels of genetic diversity in populations as well as their uniqueness.…”

Inferring spatial structure from population genetics and spatial synchrony in demography of Baltic Sea fishes: implications for management

“…; Hawkins et al . ) that broadly can be divided into three categories: (i) Molecular methods – relying on DNA/RNA or proteins; (ii) Demographic characters – population growth rates, harvest rates and age‐size distributions; and (iii) Individual phenotypic traits – morphometrics, size at age, size/age at maturation, geochemical markers, dispersal from tagging, parasite fauna (Begg and Waldman ; Bohonak ; Welch et al . ).…”

“…; Hawkins et al . ). There are several studies inferring spatial structures of species using different methods (Reiss et al .…”

Exploitation promotes earlier sex change in a protandrous patellid limpet, Patella aspera Röding, 1798

“…Inbreeding coefficients (F IS ) for P. aspera in the Macaronesia (Faria et al., ) do suggest a relative small effective population size, which could be an indication of the lack of large females as a result of size exploitation. Moreover, the latter (Faria et al., ) also showed significant genetic variation between populations of P. aspera among Macaronesian archipelagos, which is of applied interest for the definition and management of limpet stocks (Hawkins et al., ).…”